1. Field of the Invention
The present invention relates to a wastewater treatment technique, in particular to a method and system for wastewater treatment, in which the residual temperature is utilized in the reaction with a reactant to reduce the consumption of energy.
2. Related Art
Generally, for the treatment of organic wastewater, a treatment technique that is technically effective and economically feasible must be selected according to the properties of base and contaminants, so as to achieve a better effect. According to the properties of the contaminants, the treatment methods are different, and taking the treatment of wastewater containing organic contaminants as an example, many commonly used single treatment techniques can be used. Based on the features of the treatment techniques, they can be summarized as: (1) biological treatment, such as, bacteria decomposition; (2) chemical treatment, such as, chemical precipitation and oxidative decomposition; (3) thermal treatment, such as, incineration and plasma treatment; and (4) physical treatment, such as, filtration and separation. If further summarized according to the state of organic contaminants in the wastewater after treatment, in the treatment methods (1), (2), and (3), the organics in the wastewater are directly decomposed or broken down into non-toxic and decomposable organics, or the chemical structure is completely decomposed or broken down into carbon dioxide, water, and inorganics, for example, as described in U.S. Pat. No. 5,820,761, U.S. Pat. No. 6,010,632, and U.S. Pat. No. 4,604,214, which utilize wet oxidation, supercritical water oxidation, and Fentons reagent oxidation to decompose or break down the organic components in the wastewater, respectively, and are invention applications of such a treatment mode. This treatment mode has the advantage that the organic contaminants can be decomposed into CO2, H2O, and other low-molecular substances (such as, acids, or simple hydrocarbons) effectively through a high-temperature, high-pressure reaction or oxidation initiated by OH free radical. However, it is necessary to remove the added chemical reagents to avoid the generation of secondary wastewater, and prevent from being decomposed into more toxic organics during the reaction.
As to the treatment method (4), the organic components that are difficult to decompose and have high toxicity are separated from the wastewater by separation method, thus making the wastewater meet the requirements of the discharge standard. During the treatment, no changes in the structure of the organics occur, for example, as described in U.S. Pat. No. 6,319,412 and U.S. Pat. No. 6,379,555, which disclose use of fixed-bed activated carbon adsorption to remove the organic components in wastewater, and then further treatment with other methods, and are invention applications of such a treatment mode. The main advantage of this treatment mode is that no chemicals is added, thus avoiding the problem of secondary wastewater, and the concentrated liquid or sludge obtained by separation is significantly reduced in volume, and can be further treated by incineration or solidification.
In recent years, due to the rapid development of science and technology, wastewaters from different industries get more diversified and may contain complex and non-biodegradable compounds, thus single treatment technique cannot solve the problem completely. If a wastewater contains various high-boiling point organics simultaneously, and the water content is high, then the treatment will get more difficult. As for the current high-tech industry, such as, semiconductor manufacturing, various wastewaters can be generated in the processes, for example, wafer cleaning wastewater, photoresist removal wastewater, wet etching wastewater, polishing wastewater, cutting wastewater, exchange medium or adsorbent regeneration wastewater. Taking wastewater from the condensed liquid of volatile organic compound (VOC) waste gas treatment system and zeolite adsorbent regeneration during the photoresist removal process as example, it mainly contains high-boiling point organic solvents, such as, dimethyl sulfoxide (DMSO), monoethanol amine (MEA), and N-methyl pyrrolidone (NMP), and small amount of low-boiling point organic solvents, such as, isopropyl alcohol (IPA) and acetone, and the total organic carbon (TOC) concentration is about 8,000˜16,000 mg/L. Generally, the wastewater is temporarily stored in the factory or treated by incineration by authorizing substitute wastewater treatment enterprise in the industry. However, as the water content is extremely high (>90%), directly incineration will increase both the energy consumption and the discharge of carbon dioxide, thus resulting in another environmental protection problem.
For another example, in the material manufacturers, after the heat treatment of plastic sleeve, the wastewater generated by cleaning the sleeve wall contains ethylene glycol (b.p.=197.6) component used as heat medium, with an average concentration of about 0.06M. As the water content is high and the amount of the wastewater is great, with the consideration of the treatment cost, the incineration is not suitable. In the case of biological treatment, as the growth and culture of microorganisms are in very harsh environment, difficult to control, and need a long time, the biochemical oxygen demand (BOD) concentration of the wastewater after the treatment will often exceed the standard value in the regulations of environmental protection.
In prior art, distillation is mostly used to treat wastewater containing various organics, in which a distilled liquid is first generated, and next the distilled liquid is collected into a collecting tank. As organic substances still remain, the distilled liquid does not meet the requirements of the discharge standard. In order to decrease the organic carbon content, the distilled liquid will be further treated by other methods to meet the requirements of the discharge standard, for example, by secondary distillation, or biological treatment, or UV/O3 treatment, to further decrease the TOC in the distilled liquid. Although this can address the above demand in the industry, multiple distillations will consume more energy. Moreover, for biological treatment or UV/O3 treatment, the equipment cost is high, and the treatment time is very long, and as a result, the economic effect is low.
Therefore, there is still a need for a new system and method for wastewater treatment to reduce the treatment cost, improve the treatment efficiency, and simplify the treatment process, in order to meet the demand in the industry.